Prognostic value of olfactory evoked potentials in patients with post-infectious olfactory dysfunction

Olfactory event-related potentials (OERPs) and trigeminal event-related potentials (TERPs) - a pilot study in Czech participants with normal sense of smell

INTRODUCTION

In recent years, the evaluation of potential events related to olfactory events (OERPs) and trigeminal events (TERPs) has become increasingly important in the diagnosis of olfactory disorders. This technique is increasingly used in basic research and clinical practice to evaluate people suffering from olfactory disorders.

PURPOSE OF THE STUDY

In a pilot project of the first investigations of OERPs and TERPs in the Czech Republic, we analyse the event-related potentials of the data of normosmic participants.

METHODS

In the prospective study, 21 normosmic participants were enrolled for a 2-year period (5/2021-5/2023). OERPs/TERPs were recorded at the scalp vertex (electrode Pz/Cz). Odourants 2-phenylethanol/CO2 were used to selectively activate Nervus olfactorius/ Nervus trigeminus. Brain responses to olfactory/trigeminal stimuli (EEG) were recorded in 21/18 normosmic subjects.

RESULTS

In the statistical analysis of the olfactory interval N1-P2 (age, gender), we found no statistically significant differences. In the statistical analysis of the trigeminal interval N1-P2 (age, gender) we found statistically significant differences in amplitude by gender (male amplitudes were higher than female amplitudes, p = 0.006).

CONCLUSION

Our pilot data can function very well as an internal guide for ongoing and future olfactory research studies. Evaluation of the presence of OERPs appears to be an important parameter for the evaluation of olfactory disorders. The absence of OERPs is a strong indicator of the presence of olfactory dysfunction.

The PEA Bead Test as a Screening Tool for Olfactory Dysfunction: A Preliminary Study

This study, conducted in a single tertiary hospital, aimed to evaluate the 2-phenylethyl alcohol (PEA)-based sniffing bead test as a screening tool for olfactory dysfunction suitable for implementation in otorhinolaryngology and other settings, including general practice clinics. A total of 139 patients were enrolled, all of whom underwent both the PEA bead test and conventional psychophysical olfactory function testing. Characteristics such as age, sex, concurrent diseases, smoking history, and presence of gustatory dysfunction were reviewed. Statistical analyses included receiver operating characteristic curve analysis, area under the curve determination, and multivariate linear regression guided by the Akaike information criterion. Significant correlations were found between the PEA bead test and various subsets of the conventional YSK olfactory function test: threshold (r = 0.631), discrimination (r = 0.455), and identification (r = 0.596), as well as the composite threshold-discrimination-identification score (r = 0.686). These correlations remained significant even when adjusting for other clinical characteristics. The PEA bead test showed a sensitivity of 0.778 and a specificity of 0.958 for discriminating olfactory dysfunction at a cutoff value of ≥1. These findings indicate that the PEA bead test could be a valuable screening tool for olfactory dysfunction across diverse clinical settings. Further large-scale, multicenter research is recommended to confirm these preliminary results.

Olfactory dysfunction in chronic rhinosinusitis: insights into the underlying mechanisms and treatments

INTRODUCTION

Olfactory dysfunction (OD) is a typical symptom of chronic rhinosinusitis (CRS), which adversely affects the patient's quality of life and results in mood depression. Studies investigating the impairment of olfactory epithelium (OE) have indicated that inflammation-induced cell damage and dysfunction in OE plays a vital role in the development of OD. Consequently, glucocorticoids and biologics are beneficial in the management of OD in CRS patients. However, the mechanisms underlying OE impairment in CRS patients have not been fully elucidated.

AREAS COVERED

This review focuses on mechanisms underlying inflammation-induced cell impairment in OE of CRS patients. Additionally, the methods used for detection of olfaction and both currently available and potentially new clinical treatments for OD are reviewed.

EXPERT OPINION

Chronic inflammation in OE impairs not only olfactory sensory neurons but also non-neuronal cells that are responsible for regeneration and support for neurons. The current treatment for OD in CRS is mainly aimed at attenuating and preventing inflammation. Strategies for use of combinations of these therapies may achieve greater efficacy in restoration of the damaged OE and consequently better management of OD.

Design and Evaluation of a Potential Non-Invasive Neurostimulation Strategy for Treating Persistent Anosmia in Post-COVID-19 Patients

A new pandemic was declared at the end of 2019 because of coronavirus disease 2019 (COVID-19). One of the effects of COVID-19 infection is anosmia (i.e., a loss of smell). Unfortunately, this olfactory dysfunction is persistent in around 5% of the world's population, and there is not an effective treatment for it yet. The aim of this paper is to describe a potential non-invasive neurostimulation strategy for treating persistent anosmia in post-COVID-19 patients. In order to design the neurostimulation strategy, 25 subjects who experienced anosmia due to COVID-19 infection underwent an olfactory assessment while their electroencephalographic (EEG) signals were recorded. These signals were used to investigate the activation of brain regions during the olfactory process and identify which regions would be suitable for neurostimulation. Afterwards, 15 subjects participated in the evaluation of the neurostimulation strategy, which was based on applying transcranial direct current stimulation (tDCS) in selected brain regions related to olfactory function. The results showed that subjects with lower scores in the olfactory assessment obtained greater improvement than the other subjects. Thus, tDCS could be a promising option for people who have not fully regained their sense of smell following COVID-19 infection.

Assessment and Scientific Progresses in the Analysis of Olfactory Evoked Potentials

The human sense of smell is important for many vital functions, but with the current state of the art, there is a lack of objective and non-invasive methods for smell disorder diagnostics. In recent years, increasing attention is being paid to olfactory event-related potentials (OERPs) of the brain, as a viable tool for the objective assessment of olfactory dysfunctions. The aim of this review is to describe the main features of OERPs signals, the most widely used recording and processing techniques, and the scientific progress and relevance in the use of OERPs in many important application fields. In particular, the innovative role of OERPs is exploited in olfactory disorders that can influence emotions and personality or can be potential indicators of the onset or progression of neurological disorders. For all these reasons, this review presents and analyzes the latest scientific results and future challenges in the use of OERPs signals as an attractive solution for the objective monitoring technique of olfactory disorders.

[Application research and development of objective examination of olfactory function]

The sense of smell is one of the five most primitive human sensory functions, and it plays a very important role in our daily lives. Despite numerous methods for evaluating olfactory function, there is still a lack of standardization of olfactory tests and the results are often inconsistent. Furthermore, the related research on objective evaluation started relatively late. Along with the deciphering of the olfactory pathway, the technical level of olfactory objective inspection has been greatly improved and significant progress has also been made in terms of clinical application, such as: olfactory pathway MRI and fMRI imaging, OERPs, BEAM for various olfactory disorders and early diagnosis of neurodegenerative disorders, as well as related research based on bionic olfactory sensing technology. This article mainly introduces the recent research progress of several commonly used objective olfactory tests and provides reference for more accurate evaluation of olfactory function.